The Islands Provincial Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Islands Provincial Park clear sky chart from 2005-11-06 to 2026-10-29.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	21% 11% 4 8% 5% 4 4 3 5% 6% 30%	150832
	Night	21% 12% 4 9% 5% 4 4 3 4 6% 28%	141362
Transparency	Day	54% 3 11% 20% 11% 1	154412
	Night	56% 3 10% 20% 11% 1	145859
Seeing	Day	28% 16% 32% 17% 6% 1	19873
	Night	27% 14% 29% 22% 7% 1	27306

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	17% 17% 7% 19% 6% 4 4 3 4 5% 15%	4723
	11th to 20th	Day	18% 17% 8% 20% 7% 5% 4 3 3 4 10%	5247
	21st to end	Day	16% 13% 5% 15% 10% 6% 5% 4 4 5% 16%	5781
February	1st to 10th	Day	19% 17% 5% 11% 7% 6% 5% 3 4 4 18%	1890
	11th to 20th	Day	18% 11% 5% 13% 7% 5% 4 3 5% 6% 22%	1843
	21st to end	Day	15% 14% 4 9% 6% 4 4 3 6% 7% 28%	1652
March	1st to 10th	Day	25% 15% 4 10% 6% 4 4 3 4 4 20%	4991
	11th to 20th	Day	18% 19% 4 7% 4 4 4 3 4 5% 28%	5090
	21st to end	Day	29% 12% 5% 10% 5% 4 4 2 3 4 21%	5587
April	1st to 10th	Day	25% 16% 3 7% 4 4 3 2 4 5% 28%	2437
	11th to 20th	Day	21% 11% 3 6% 4 4 4 3 4 6% 34%	2634
	21st to end	Day	24% 9% 2 6% 4 3 3 3 5% 6% 35%	2730
May	1st to 10th	Day	29% 12% 3 8% 3 3 3 2 4 5% 27%	7639
	11th to 20th	Day	21% 11% 3 7% 4 4 4 3 5% 6% 32%	7981
	21st to end	Day	21% 11% 3 9% 5% 4 4 3 5% 6% 29%	9059
June	1st to 10th	Day	25% 9% 2 6% 4 4 4 3 5% 7% 32%	2940
	11th to 20th	Day	21% 9% 3 5% 4 3 3 3 5% 6% 37%	3108
	21st to end	Day	26% 8% 2 5% 5% 4 4 4 5% 8% 29%	3150
July	1st to 10th	Day	25% 9% 3 7% 4 4 4 4 5% 7% 29%	8844
	11th to 20th	Day	23% 9% 2 5% 3 4 4 3 5% 8% 35%	8142
	21st to end	Day	19% 8% 3 6% 4 4 4 3 5% 8% 36%	8342
August	1st to 10th	Day	24% 9% 3 6% 3 3 3 3 5% 7% 34%	6015
	11th to 20th	Day	18% 8% 3 7% 4 4 4 3 5% 7% 37%	5953
	21st to end	Day	15% 7% 2 6% 4 4 4 3 5% 8% 43%	6435
September	1st to 10th	Day	17% 7% 3 5% 4 4 3 3 5% 7% 43%	2520
	11th to 20th	Day	18% 6% 3 5% 3 4 3 3 4 5% 46%	2331
	21st to end	Day	20% 8% 2 5% 4 4 3 3 4 6% 41%	2308
October	1st to 10th	Day	19% 7% 2 5% 4 4 4 3 4 7% 41%	2100
	11th to 20th	Day	20% 7% 3 7% 4 5% 5% 4 5% 7% 34%	2100
	21st to end	Day	20% 9% 3 7% 5% 4 5% 3 4 6% 33%	2276
November	1st to 10th	Day	21% 10% 3 6% 5% 3 4 4 5% 6% 33%	1788
	11th to 20th	Day	21% 14% 4 8% 6% 4 4 3 5% 7% 25%	1680
	21st to end	Day	20% 14% 3 9% 6% 5% 5% 4 4 5% 23%	1680
December	1st to 10th	Day	24% 12% 4 13% 4 4 4 3 5% 6% 20%	2690
	11th to 20th	Day	29% 11% 3 8% 5% 4 4 3 4 6% 22%	3076
	21st to end	Day	21% 15% 6% 8% 4 4 3 3 4 5% 27%	4070
January	1st to 10th	Night	15% 17% 7% 21% 6% 5% 4 3 4 4 14%	8197
	11th to 20th	Night	21% 14% 6% 16% 6% 5% 4 3 5% 5% 15%	7638
	21st to end	Night	14% 13% 5% 16% 8% 7% 6% 4 5% 6% 18%	8400
February	1st to 10th	Night	19% 14% 5% 11% 7% 5% 5% 4 5% 5% 21%	2730
	11th to 20th	Night	17% 11% 4 11% 8% 6% 5% 4 5% 7% 22%	2663
	21st to end	Night	14% 12% 5% 7% 6% 5% 5% 4 5% 7% 30%	2149
March	1st to 10th	Night	24% 14% 5% 9% 7% 5% 4 3 3 4 22%	5068
	11th to 20th	Night	19% 15% 5% 8% 4 3 4 4 5% 6% 26%	5089
	21st to end	Night	31% 11% 4 7% 3 2 2 2 4 5% 28%	5587
April	1st to 10th	Night	24% 13% 3 7% 4 3 3 2 5% 5% 30%	2181
	11th to 20th	Night	25% 10% 2 5% 3 4 3 3 4 7% 33%	1931
	21st to end	Night	23% 10% 3 6% 4 3 4 3 4 7% 33%	1890
May	1st to 10th	Night	30% 14% 3 6% 3 3 3 3 4 5% 26%	5259
	11th to 20th	Night	25% 13% 3 7% 3 3 3 3 4 5% 33%	4896
	21st to end	Night	19% 14% 3 8% 5% 4 3 3 4 5% 32%	5147
June	1st to 10th	Night	25% 8% 3 7% 3 3 4 3 4 8% 31%	1680
	11th to 20th	Night	20% 11% 3 7% 4 4 4 3 5% 6% 35%	1526
	21st to end	Night	27% 10% 3 6% 4 4 4 3 5% 6% 27%	1470
July	1st to 10th	Night	26% 10% 4 7% 4 4 4 4 5% 8% 24%	4110
	11th to 20th	Night	26% 10% 2 5% 4 4 3 3 4 6% 32%	4795
	21st to end	Night	22% 9% 2 7% 4 4 4 3 5% 7% 34%	5736
August	1st to 10th	Night	26% 10% 3 7% 4 4 3 3 4 6% 30%	4135
	11th to 20th	Night	19% 11% 2 7% 5% 4 4 2 5% 7% 35%	4092
	21st to end	Night	18% 10% 3 6% 3 4 4 3 5% 7% 39%	4690
September	1st to 10th	Night	18% 7% 2 5% 4 4 3 4 5% 7% 40%	2100
	11th to 20th	Night	19% 6% 2 4 3 3 3 3 5% 6% 46%	2284
	21st to end	Night	22% 8% 3 6% 3 3 3 3 5% 6% 38%	2311
October	1st to 10th	Night	20% 7% 3 5% 4 4 4 3 4 6% 41%	2520
	11th to 20th	Night	20% 8% 2 5% 3 4 3 3 4 6% 41%	2520
	21st to end	Night	22% 8% 2 6% 3 4 4 3 4 7% 36%	2737
November	1st to 10th	Night	19% 7% 3 6% 4 4 4 3 5% 6% 38%	2728
	11th to 20th	Night	20% 11% 3 8% 6% 5% 5% 4 5% 7% 27%	2940
	21st to end	Night	20% 13% 3 8% 4 4 5% 4 6% 6% 27%	2940
December	1st to 10th	Night	16% 12% 4 12% 6% 5% 5% 4 5% 7% 22%	4720
	11th to 20th	Night	24% 12% 3 7% 4 4 4 4 5% 6% 27%	5353
	21st to end	Night	23% 12% 4 9% 6% 4 3 3 4 4 28%	7150

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	69% 3 10% 14% 4	4724
	11th to 20th	Day	75% 3 8% 10% 4	5280
	21st to end	Day	65% 3 8% 13% 10% 1	5781
February	1st to 10th	Day	65% 3 10% 13% 7% 1	1890
	11th to 20th	Day	60% 3 10% 18% 8% 1	1851
	21st to end	Day	53% 4 11% 21% 9% 2	1652
March	1st to 10th	Day	66% 2 8% 13% 9% 2	4995
	11th to 20th	Day	57% 2 14% 17% 9% 1	5090
	21st to end	Day	66% 2 6% 15% 10% 1	5587
April	1st to 10th	Day	58% 2 8% 16% 14% 1	2437
	11th to 20th	Day	51% 4 9% 21% 13% 1	2634
	21st to end	Day	49% 3 11% 21% 14% 2	2730
May	1st to 10th	Day	62% 2 9% 18% 8%	7651
	11th to 20th	Day	54% 3 12% 20% 9% 1	7985
	21st to end	Day	55% 3 12% 16% 12% 1	9060
June	1st to 10th	Day	53% 3 10% 22% 12% 1	2940
	11th to 20th	Day	49% 3 10% 22% 14% 2	3108
	21st to end	Day	55% 4 14% 17% 10% 1	3150
July	1st to 10th	Day	55% 4 12% 18% 10% 1	8769
	11th to 20th	Day	49% 4 9% 27% 11%	8066
	21st to end	Day	45% 4 13% 23% 14%	8159
August	1st to 10th	Day	51% 4 11% 23% 10% 1	6002
	11th to 20th	Day	45% 5% 14% 28% 8%	5992
	21st to end	Day	40% 4 12% 26% 17% 1	6435
September	1st to 10th	Day	42% 3 11% 25% 17% 2	2520
	11th to 20th	Day	40% 3 10% 25% 19% 3	2331
	21st to end	Day	45% 3 7% 23% 18% 3	2308
October	1st to 10th	Day	42% 6% 11% 26% 14% 1	3360
	11th to 20th	Day	41% 3 9% 24% 21% 1	3340
	21st to end	Day	44% 4 11% 25% 12% 4	3602
November	1st to 10th	Day	51% 3 13% 22% 10% 1	1788
	11th to 20th	Day	57% 4 11% 19% 9%	1680
	21st to end	Day	60% 4 12% 19% 5% 1	1680
December	1st to 10th	Day	62% 4 12% 19% 4	2690
	11th to 20th	Day	62% 3 11% 14% 10% 1	3075
	21st to end	Day	58% 2 12% 18% 10% 1	4070
January	1st to 10th	Night	70% 3 8% 14% 4	8197
	11th to 20th	Night	68% 4 9% 15% 5%	7680
	21st to end	Night	61% 3 10% 15% 10%	8400
February	1st to 10th	Night	63% 3 11% 15% 7% 1	2730
	11th to 20th	Night	58% 3 10% 20% 8% 1	2666
	21st to end	Night	52% 3 11% 22% 11% 1	2149
March	1st to 10th	Night	65% 3 7% 12% 12% 1	5077
	11th to 20th	Night	60% 2 13% 17% 7% 1	5090
	21st to end	Night	60% 2 7% 19% 11% 1	5587
April	1st to 10th	Night	58% 2 8% 16% 13% 3	2181
	11th to 20th	Night	51% 3 8% 24% 12% 1	1931
	21st to end	Night	52% 3 9% 21% 12% 2	1890
May	1st to 10th	Night	64% 1 9% 17% 9%	5265
	11th to 20th	Night	56% 2 9% 21% 10% 2	4897
	21st to end	Night	56% 3 9% 22% 10%	5148
June	1st to 10th	Night	53% 2 8% 27% 10%	1680
	11th to 20th	Night	51% 3 11% 21% 13% 1	1526
	21st to end	Night	60% 4 9% 16% 11% 1	1470
July	1st to 10th	Night	60% 5% 11% 18% 7%	4075
	11th to 20th	Night	55% 4 7% 19% 14% 1	4748
	21st to end	Night	52% 5% 8% 21% 13% 2	5605
August	1st to 10th	Night	57% 3 10% 20% 10%	4123
	11th to 20th	Night	50% 4 14% 25% 6%	4119
	21st to end	Night	46% 4 10% 25% 15% 1	4689
September	1st to 10th	Night	44% 3 8% 26% 16% 3	2100
	11th to 20th	Night	40% 3 7% 27% 20% 2	2284
	21st to end	Night	49% 2 6% 25% 17% 2	2311
October	1st to 10th	Night	45% 5% 10% 24% 14% 2	4040
	11th to 20th	Night	36% 3 10% 26% 24% 1	4019
	21st to end	Night	41% 2 11% 28% 16% 2	4349
November	1st to 10th	Night	47% 3 14% 24% 12% 1	2728
	11th to 20th	Night	54% 3 12% 20% 10%	2940
	21st to end	Night	54% 5% 15% 18% 7%	2940
December	1st to 10th	Night	56% 4 12% 23% 5%	4720
	11th to 20th	Night	56% 3 12% 16% 12% 1	5355
	21st to end	Night	59% 2 10% 18% 10% 1	7150

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	31% 26% 27% 13% 3	430
	11th to 20th	Day	33% 21% 29% 14% 3	430
	21st to end	Day	23% 28% 31% 15% 3	473
February	1st to 10th	Day	30% 23% 29% 14% 4	430
	11th to 20th	Day	31% 24% 28% 14% 3	426
	21st to end	Day	28% 21% 34% 14% 2	406
March	1st to 10th	Day	33% 21% 34% 10% 2	540
	11th to 20th	Day	31% 23% 31% 10% 4 1	540
	21st to end	Day	31% 23% 31% 10% 5% 1	594
April	1st to 10th	Day	35% 24% 29% 10% 1	540
	11th to 20th	Day	30% 21% 36% 11% 2	532
	21st to end	Day	29% 21% 33% 12% 4 1	540
May	1st to 10th	Day	31% 21% 33% 12% 2 1	543
	11th to 20th	Day	28% 18% 32% 18% 4 1	689
	21st to end	Day	30% 14% 33% 17% 6% 1	845
June	1st to 10th	Day	30% 11% 34% 19% 5% 1	780
	11th to 20th	Day	25% 13% 33% 21% 7% 1	780
	21st to end	Day	32% 9% 32% 20% 5% 1	780
July	1st to 10th	Day	28% 7% 31% 24% 8% 1	770
	11th to 20th	Day	28% 7% 32% 22% 10% 1	721
	21st to end	Day	23% 8% 36% 25% 8% 1	620
August	1st to 10th	Day	19% 8% 37% 26% 9% 1	566
	11th to 20th	Day	23% 9% 33% 22% 11% 2	559
	21st to end	Day	21% 10% 35% 21% 11% 3	627
September	1st to 10th	Day	20% 11% 34% 26% 7% 2	570
	11th to 20th	Day	22% 11% 32% 22% 10% 3	570
	21st to end	Day	22% 13% 36% 20% 7% 2	568
October	1st to 10th	Day	22% 11% 33% 21% 10% 2	450
	11th to 20th	Day	22% 18% 32% 21% 6% 2	450
	21st to end	Day	24% 18% 35% 16% 6% 1	486
November	1st to 10th	Day	25% 20% 32% 16% 7% 1	425
	11th to 20th	Day	31% 24% 27% 12% 6%	430
	21st to end	Day	30% 22% 27% 16% 3	430
December	1st to 10th	Day	37% 18% 29% 14% 3	430
	11th to 20th	Day	39% 25% 23% 11% 3	430
	21st to end	Day	31% 23% 28% 14% 3 1	473
January	1st to 10th	Night	28% 23% 30% 15% 4	944
	11th to 20th	Night	30% 17% 29% 21% 3	840
	21st to end	Night	24% 24% 31% 17% 4	924
February	1st to 10th	Night	28% 21% 28% 20% 2	840
	11th to 20th	Night	26% 23% 33% 16% 2	823
	21st to end	Night	23% 18% 35% 18% 6%	692
March	1st to 10th	Night	28% 19% 33% 17% 3	840
	11th to 20th	Night	25% 18% 32% 19% 6%	840
	21st to end	Night	26% 19% 32% 17% 5%	924
April	1st to 10th	Night	32% 14% 33% 18% 3	711
	11th to 20th	Night	31% 13% 37% 16% 3 1	624
	21st to end	Night	30% 10% 30% 22% 7% 1	630
May	1st to 10th	Night	33% 11% 33% 18% 4	630
	11th to 20th	Night	29% 10% 32% 23% 5% 1	622
	21st to end	Night	29% 8% 32% 24% 6% 1	682
June	1st to 10th	Night	28% 7% 33% 26% 5%	630
	11th to 20th	Night	25% 7% 31% 31% 7%	476
	21st to end	Night	33% 3 28% 29% 7%	420
July	1st to 10th	Night	30% 3 27% 30% 9% 1	410
	11th to 20th	Night	28% 4 28% 30% 10%	597
	21st to end	Night	29% 4 27% 33% 7%	689
August	1st to 10th	Night	21% 4 29% 35% 10% 1	628
	11th to 20th	Night	22% 6% 24% 34% 13% 1	622
	21st to end	Night	23% 5% 25% 29% 16% 2	693
September	1st to 10th	Night	20% 7% 29% 32% 10% 2	630
	11th to 20th	Night	22% 6% 26% 27% 16% 3	814
	21st to end	Night	27% 8% 26% 25% 13% 2	840
October	1st to 10th	Night	25% 9% 29% 26% 10% 1	840
	11th to 20th	Night	24% 16% 26% 24% 9% 2	840
	21st to end	Night	27% 16% 27% 24% 6%	913
November	1st to 10th	Night	26% 14% 28% 23% 8% 1	853
	11th to 20th	Night	26% 19% 29% 20% 6%	950
	21st to end	Night	28% 21% 27% 17% 6%	950
December	1st to 10th	Night	31% 17% 29% 18% 5%	950
	11th to 20th	Night	32% 24% 28% 14% 3	950
	21st to end	Night	30% 22% 26% 17% 4	1045

Page generated at 2026-10-26 05:37:50. Version ac07

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